The Samsung Galaxy S smartphone series has attracted rabid fans, with older-generation models keeping a residual value that rivals that of older-generation Apple iPhones.

Samsung Galaxy S 4

The Samsung Galaxy S smartphone series has attracted rabid fans, with older-generation models keeping a residual value that rivals that of older-generation Apple iPhones, officials at trade-in site NextWorth said this week.

The value of many older smartphone models can drop significantly when re-sold, but both iPhones and Galaxy S smartphones do well for original owners with a residual value decline of about 5% a month, NextWorth officials said.

With the expected launch of the Galaxy S 4 on Thursday, the previous GS III should see a residual value decline of 5% a month, NextWorth said. When the Galaxy S III launched in 2012, NextWorth said it saw value declines of about 5% for both the original Galaxy S and the Galaxy S II.

"This kind of value decline before, during and after a new product release is something we have historically only seen with iPhone launches," said Jeff Trachsel, chief marketing officer at NextWorth. "It is one more indication that Samsung is creating a similar franchise with the fourth Galaxy, where new models are rabidly sought by owners of older generations."

NextWorth looked at the average selling price decline for used Galaxy S and SII smartphones from April to August of 2012 in reaching its conclusion.

When the Galaxy S III was announced in May of 2012, both previous generations declined in value by 5% from the prior month. NextWorth said the average price of a used Galaxy S was $180 in April 2012, while the used S II averaged $334.

By the time the SIII was released in June, the two prior devices lost another 6% or 7% of value, NextWorth said.

The new GS4 is expected to cost about $200 with a two-year contract. The $200 figure has been the subsidized price for the previous Galaxy S III when it was new on all the major U.S. carriers.

Unlocked prices for the new Galaxy S devices have been about $650.

Used Samsung Galaxy SII devices showed up Thursday on eBay selling for $250 to $350, but some of the bids were far less, as low as $44.